Field of Invention
The present invention relates to an image processing method and an image processing system; particularly, it relates to such image processing method and image processing system capable of assigning different gains to different pixel array sections.
Description of Related Art
Please refer to FIG. 1, which shows a block diagram of a conventional image processing system. The image processing system 10 comprises an image sensor 19 and a processor 13. The image sensor 19 includes a pixel array 11 and an automatic gain control (AGC) unit 12. In an enable phase TAVG_EN, the processor 13 provides an enable signal TAVG_EN to the pixel array 11 and the AGC unit 12, whereby the pixel array 11 generates background determination signals S-VRST and S-VRSTD and the AGC unit 12 generates a PWM signal TAVG according to the signals S-VRST and S-VRSTD, to determine a background illumination level which for example relates to an ambient light intensity; the functions of the signals S-VRST, S-VRSTD and TAVG will be explained later with reference to FIGS. 2 and 3. In a shutter phase, the processor 13 provides a shutter signal SHU to control the timing and duration in which the pixel array 11 is exposed by light emitted from a light source 1 and reflected by an object (not shown), whereby the pixel array 11 generates an image signal (not shown) according to an image of the object. The processor 13 also provides a lighting control signal L_Ctl to control the light source 1 such that the light source 1 emits light at designated timings.
FIG. 2 shows a pixel circuit of one pixel unit. As shown in FIG. 2, a pixel unit includes a photo current generator 110 which generates a current I in response to light, a capacitor 111, a TAVG_EN PMOS switch 117 for pull up, and a shutter switch 118. The photo current generator 110 is for example as shown, including a BJT (bipolar junction transistor) 115 which generates the current I in response to light, a current source 112, and MOS transistors 113 and 116 to bias the base voltage of the BJT and acts as common gate respectively.
FIG. 3 shows waveforms of the signals shown in FIG. 1. Please refer to FIGS. 2-3 in conjugation with FIG. 1. Before the enable phase TAVG_EN (low state), the enable signal TAVG_EN closes the PMOS switch 117, and the node VRST is pulled to a level corresponding to the voltage supply VDDA, which is the background determination signal S-VRSTD. In the enable phase TAVG_EN, the enable signal TAVG_EN opens the PMOS switch 117, and the capacitor 111 discharges, until the voltage across the capacitor 111 drops a predetermined level V_threshold, and this dropping waveform is the background determination signal S-VRST. The timing when the background determination signal S-VRST drops the level V_threshold (i.e., when the background determination signal S-VRST reaches a level which is equal to S-VRSTD minus V_threshold) determines the PWM signal TAVG. The PWM signal TAVG can be regarded as a gain control signal. Based on the information of the PWM signal TAVG, the processor 13 determines the pulse width of the shutter signal SHU.
The pixel array 11 includes multiple pixel units. Conventionally, the gain control signal provided by the AGC unit 12 is the same for every pixel unit in the pixel array 11.
However, the pixel array 11 may not be uniformly illuminated under certain circumstances, and because the PWM signal TAVG and the signal SHU is the same for every pixel unit in the pixel array 11, this prior art cannot obtain complete and sufficient information of the pixel array 11 because certain pixel units may be underexposed or overexposed.
In view of the above, to overcome the drawback in the prior art, the present invention proposes an image processing method and image processing system capable of assigning different gains to different pixel array sections.